German Pat. No. 2,102,103 discloses a field-effect diode structure having a p- type substrate with an n- type epitaxial layer grown on top of the substrate. The substrate can be replaced by an insulating material. A first p+ type anode region, a second p+ type gate region, and an n+ type cathode region exist within portions of the epitaxial layer and each forms a portion of a common surface of the epitaxial layer. The three regions are separated from each other by portions of the epitaxial layer. The patent states that conduction between anode and cathode can only be interrupted by setting the anode voltage to a zero or negative level for a short period of time and by setting the gate voltage to a predetermined critical level. It is undesirable and/or impractical in many applications to have to adjust the anode voltage. Leakage of the diode is stated to cause it to switch on when it should be off. It is unclear how the suggested solution of a register helps solve this problem and whether or not such a register is a discrete component or can be integrated on the same substrate as the diode. It is also unclear how to physically and electrically isolate the diode from other components on the common substrate.
In an article entitled "A Field Terminated Diode" by Douglas E. Houston et al, published in IEEE Transactions on Electron Devices, Vol. ED-23, No. 8, August 1976, and in U.S. Pat. No. 4,060,821 (Douglas E. Houston et al), issued Nov. 29, 1977, there is described a discrete solid-state high voltage switch that has a vertical geometry and which includes a region that can be pinched off to provide an "OFF" state or which can be made highly conductive with dual carrier injection to provide an "ON" state. One problem with this switch is that it is not easily manufacturable with other like switching devices on a common substrate. Another problem is that the spacing between the grids and the cathode should be small to limit the magnitude of the control grid voltage; however, this limits the useful voltage range because it decreases grid-to-cathode breakdown voltage. This limitation effectively limits the use of two of the devices with the cathode of each coupled to the anode of the other to relatively low voltages. Such a dual device structure would be useful as a high voltage bidirectional solid-state switch. An additional problem is that the base region should ideally be highly doped to avoid punch-through from the anode to the grid; however, this leads to a low voltage breakdown between anode and cathode. Widening of the base region limits the punch-through effect; however, it also increases the resistance of the device in the "ON" state.
It is desirable to have a solid-state switch which is easily integratable such that two or more switches can be simultaneously fabricated on a common substrate and wherein each switch is adapted such that one terminal thereof controls its state and each switch is capable of bilateral blocking of relatively high voltages and breaking current. One such structure is described in copending U.S. patent application Ser. Nos. 972,056 and 107,774, filed Dec. 20, 1978 and Dec. 28, 1979, respectively, and in copending U.S. patent application Ser. No. 248,192, filed Mar. 27, 1981. All of these applications have a common assignee. This present application relates to a subsequent improvement in such structures.